1. Field
Example embodiments relate to a functionalized metal nanoparticle, a buffer layer including the functionalized metal nanoparticle and an electronic device including the buffer layer. Other example embodiments relate to a functionalized metal nanoparticle, a buffer layer including the functionalized metal nanoparticle, which may improve the injection and mobility of electrons or holes, may form ohmic contacts, and may improve the selectivity between electrodes and the buffer layer at the time of forming the buffer layer on the electrodes and an electronic device including the buffer layer.
2. Description of the Related Art
Organic material-based device technologies may supplement silicon based electronic devices in the field of relatively large-sized flexible displays. The technologies for manufacturing organic thin film transistors (OTFTs), which are being researched, may be sufficiently competitive in the fields of integrity and performance with silicon thin film transistors.
The infrastructure costs for manufacturing organic thin film transistors (OTFTS) are only about ⅓ of those for manufacturing amorphous silicon thin film transistors, and the organic thin film transistors (OTFTS) may be more easily operated and continuously processed, unlike inorganic substrates. Therefore, the process costs of the organic thin film transistors (OTFTS) are expected to decrease compared to those of conventional thin film transistors. In order to apply the organic thin film transistor (OTFT) to the backplane of a display, the design and synthesis of an organic semiconductor having increased mobility and the improvement of the characteristics of the organic thin film transistor (OTFT) through the design of devices and the development of process technologies are required.
Conventionally, a thin film transistor may include a substrate, a gate electrode, a gate insulation layer, source/drain electrodes and a semiconductor layer, and, if necessary, may further include an electron injection layer, a hole injection layer, an electron transportation layer, and a hole transportation layer.
The characteristics of a thin film transistor are determined by the injection and migration of electrons or holes. Ideally, electrons or holes are effectively injected into a channel layer without contact resistances between electrodes and a semiconductor layer, and the electrons or holes thus rapidly migrate in the channel layer. Unlike silicon thin film transistors, which may easily form ohmic contacts, in organic thin film transistors (OTFTs), the contact resistances between electrodes and a semiconductor layer may become a main cause of the deterioration of the characteristics thereof. Generally, when metals come into contact with a semiconductor layer or a charge transportation layer, having a relatively low impurity concentration, a potential barrier may be formed at the interface therebetween, so that resistance values may become increased. In principle, the height of a potential barrier may depend on the mismatch of the energy level between electrodes and a semiconductor or between electrodes and a charge transportation layer and the adhesion state therebetween.
In the contact resistances between electrodes and a semiconductor layer or between electrodes and a charge transportation layer, conventional electrode surface treatment methods used to decrease the contact resistances between electrodes and a semiconductor layer or between electrodes and a charge transportation layer include a technology of treating an electrode surface using a self-assembled monolayer (SAM) and/or a technology of treating an electrode surface using a buffer layer. Among these technologies, the technology of treating an electrode surface using a buffer layer includes forming a layer including materials for decreasing the contact resistances between electrodes and a semiconductor layer or between electrodes and a charge transportation layer, and this technology may be mainly applied to organic thin film transistors (OTFTs) or organic light emitting diodes (OLEDs).
As these buffer layer materials, low-molecular semiconductors which may be formed into a film in a vacuum process, e.g., triphenyl amine derivatives, or acid-doped conductive polymers which may be formed into a film in a solution process, e.g., poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), have been used.
Buffer layer materials that may be formed into a film in a solution process allow for cost reduction. However, when the acid-doped conductive polymers are used as the buffer layer materials, acid-dopants may be diffused to channel layers, thus decreasing the stability of the device.
With most hole transportation (P type) organic semiconductors, because the highest occupied molecular orbital (HOMO) level of organic material is above about 5.0 eV, gold (Au), having a work function of about 5.0 eV or lower, may be used for source/drain electrodes in order to form ohmic contacts. However, gold (Au) is expensive and may not be patterned well, and not suitable for use as the source/drain electrodes of the backplane of a display. As an alternative to gold (Au), research into the use of indium tin oxide (ITO) for source/drain electrodes is being conducted. However, indium tin oxide (ITO) has a work function of about 4.8 eV or lower, and the degree of the mismatch of the energy level between electrodes and a semiconductor layer is greater than that in the case of using gold (Au) for source/drain electrodes.